Adjustment of color balance in electro-phoresis by modification of particle size

ABSTRACT

THE COLOR BALANCE IN A COLOR ELECTROPHOTOGRAPHIC PROCESS IS IMPROVED BY CONTROL OF THE RELATIVE SIZES OF THE MEGRATING COLORED PARTICLES.

United States Patent w 3,745,003 ADJUSTMENT 0F COLOR BALANCE 1N ELECTRO- PHORESIS BY MODIFICATION OF PARTICLE SIZE Yaqub Moradzadeh, Saratoga, Calif., assignor to International Business Machines (Zorporation, Armonk, N.Y. No Drawing. Filed June 28, 1971, Ser. No. 157,758 Int. Cl. Gtl3g 9/00 US. Cl. 96-12 3 Claims ABSTRACT OF THE DISCLGSURE The color balance in a color electrophotographic process is improved by control of the relative sizes of the migrating colored particles.

Field of the invention The present process is concerned with color electrophotography. In particular, it is concerned with the colored particles to be used in such a process. It has now been found that improved color balance in color imaging processes can be obtained by proper control of the relative particle sizes of the migrating colored particles.

certain selected pairs, and there is thereby obtained higher quality images.

Summary of the invention The present invention is concerned with color electrophotography involving the photomigration of colored particles. For example, a mixture of a plurality of colored electrically photosensitive colored particles is dispersed in a carrier liquid placed between a pair of electrodes, at least one of which is partially transparent. When an elec trical field is imposed across the suspension and an image is projected on the suspension through the transparent electrode, a colored image made of migrated particles is observed on at least one of the electrodes.

The resulting color images obtained by use of the prior art lack adequate color balance. For instance, one color may be too subdued, or one color may be too prominent. The main object of the present invention is to provide a means for improving such color balance in the resulting color image. In this way, higher quality, more life-like images are obtained.

It has now unexpectedly been found that With a given color imaging system, each of the colors in the resulting image can be intensified or subdued by proper control of the particle size of the corresponding pigment in the suspension.

A typical system for use in color electrophotography contains a plurality of suspended pigments, generally three subtractive pigments: cyan, magenta, and yellow. It has now been found that by proper control of the particle size and by proper mixture of the proper particle size of each color, we can achieve images in which the colors are balanced so that they resemble the object being copied.

The average size of the particle units which migrate ranges from about 1 micron to about 20 microns. Such 3,745,003 Patented July 10, 1973 sizes can be obtained using varying ball milling times of from two to 48 hours. Particle size control is achieved by varying the degree of dispersion of the specific pigment. The average size of particle units which migrate ranges from about 0.1 to about 250 microns, preferably from about 1 to about 20 microns. Such sizes can be obtained by using various dispersion techniques, for example, ball milling for various lengths of time. According to electron microscope examinations, all of the pigments show particles of submicron size. The important size, however, is not the ultimate particle size, but rather the size of the particles which migrate as units. The units may be primary particles, aggregate particles, or does of primary particles.

In carrying out the process of the present invention, routine testing is initially required; tag, in a subtractive color mixing process a mixture of a cyan pigment, a magenta pigment, and a yellow pigment is used as starting material with the particle sizes of each color pigment approximately equal. The mixture is first used in an imaging system and the resulting image examined. Suppose, for example, that the resulting positive image contains too much of the cyan pigment. The process can be repeated using larger size particles of the cyan pigment and the amount of cyan in the positive image is reduced. By varying the size of the cyan pigment, the amount of photomigration of cyan under the influence of an electric field can be controlled until a true color balance is obtained. The relative sizes of each type of color particle can be adjusted on an empirical basis until the optimum for each system is found. Prior to the present invention, this technique for color balance had not been conceived.

While the invention will be particularly shown and described with reference to preferred embodiments thereof in the following examples, it will be understood by those skilled in the art that various changes in form and details may be made therein, without departing from the spirit and scope of the invention.

EXAMPLE 1 A suspension of 9% by weight of cyan, magenta and yellow pigments (3% each) in a liquid dielectric was prepared by 48 hours of ball milling. In this case cyan pigment was Monolight Fast Blue, magenta was Watchung Red B, and yellow was Algol Yellow G.C. (Numerous combinations of pigments suitable for use in the present invention are given in US. Pat. 3,384,565.)

The liquid dielectric was mineral spirits (Sohio 3440). Electron microscopic examination of the three particles showed particle size of submicron range, with average agglomerate size of approximately 3 microns as measured by a Conlter counter. A thin layer of this suspension was doctor blade coated onto the surface of an electrically grounded Nesa Glass plate; a previously cleaned one mil Mylar (duPonts brand of polyethylene terephthalate) sheet was placed on the suspension coated Nesa Glass plate. This sandwich was then exposed to a color transparency, illuminated through the glass, i.e., transmitted light. (An apparatus of this type is disclosed in IBM Technical Disclosure Bulletin, page 2454, January 1971).

The exposure and charging was simultaneous. The charging was accomplished with a scanning corona device at a rate of 4 cm./ sec. in the dark. The potential applied to the corona emitting wire was approximately -6kV. The Mylar film was peeled oil" and the positive color image formed on the Nesa Glass was dried and transferred to an image receiving medium via adhesive transfer. This image lacked adequate color balance due to insutficient green and yellow colors.

3 EXAMPLE 2 EXAMPLE 3 Example 1 was repeated except yellow particles were kept relatively large in the suspension. The resulting image was subdued noticeably in yellow.

EXAMPLE 4 In the like manner, magenta particle size was maintained relatively large with respect to cyan and yellow (that is, 2 hours ball mill for magenta compared to 48 hours for cyan and yellow); a subduing of magenta color compared to Examples 2 and 3 was observed. Much improved color balance was observed over Example 1.

EXAMPLE 5 The example of 4 was repeated except the magenta particles were ball milled for hours. Further separa-,

tion of colors could be observed in the resulting image-- blue, green, red and yellow were much more distinct and superior to the image obtained from Example 1.

What is claimed is:

1. In a color imaging photoelectrophoresis process comprising photomigration of particles in a suspension of a plurality of colored species of electrically photosensitive particles in a carrier liquid under the influence of an electric field, the improvement comprising initially testing the color balance of said suspension during photomigration under the influence of an electric field, and then enhancing one color or subduing one color by respectively reducing or increasing the size of the migrating particles of the corresponding pigment relative to the size of the migrating particles of another pigment.

2. A process as claimed in claim 1 wherein at least three different colored particles are used.

3. A process as claimed in claim 2 wherein the colored particles are cyan, magenta, and yellow.

References Cited UNITED STATES PATENTS 3,634,221 1/1972 Tulagin et al. 204181 GEORGE F. LESMES, Primary Examiner M. B. WITTENBERG, Assistant Examiner US. Cl. X.R. 96-1 R 

